AMPLIFIERS and HETERODYNES 

Radio Communication Pamphlet No. 9 


PREPARED IN THE OFFICE OF THE 
CHIEF SIGNAL OFFICER 


December, 1921 




WASHINGTON 

GOVERNMENT PRINTING OFFICE 
1922 






War Department 
Document No. 1092 
Office of The Adjutant General 


ADDITIONAL COPIES 

OF THIS PUBLICATION MAY BE PROCURED FROM 
THE SUPERINTENDENT OF DOCUMENTS 
GOVERNMENT PRINTING OFFICE 
WASHINGTON, D. C. 

AT 

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library of CONQRi'SS j 

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WAK DEPAETMENT, 
Washington, Decemher 19^ 1921. 

The following publication, entitled ‘‘Amplifiers and Heterodynes, 
Radio Communication Pamphlet Xo. 9,” is published for the informa¬ 
tion and guidance of all concerned. 

[062.1, A. G. O.] 

By order of the Secretary of War : 

JOHN J. PERSHING, 

General of the Ai'mies., 

Chief of Staff. 

Official : 

P. C. HARRIS, 

The Adjutant General. 


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TABLE OF CONTENTS. 


Paragraphs. 

Section I. Apparatus described in pamphlet_ 1 

II. Notes on care and operation of amplifiers and heterodynes_ 2-7 

HI. Amplifier set box, type BO-17_ 8-12 

IV. Amplifier set boxes, type BO-44 and BC-44-A_13-17 

V. Amplifier set box, type BO-8-A_18-22 

VI. Amplifier set box, type BO-101_23-29 

VII. Amplifier set box, type BO-103_30-34 

VIII. Heterodyne set box, type BO-104_35-42 

IX. Principles of amplifiers_43-48 

X. Principles embodied in the set boxes and their circuit dia¬ 
grams_ 49-54 

XI. Parts list of sets_55-56 

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AMPLIFIERS AND HETERODYNES. 


RADIO COMMUNICATION PAMPHLET NO. 9. 


Section I. 

APPARATUS DESCRIBED IN PAMPHLET. 

Paragraph. 

Apparatus described in pamphlet_ 1 

1. Apparatus described in pamphlet.—A radio set comprises two or 
more equipments, which together form a set and are given an SCR 
type number. Each equipment is given a type number, different 
type numbers being assigned to equipments that vary even in only 
one particular. The radio equipment, proper, described in this pam¬ 
phlet varies mainly in the set boxes. It is to be noted that some of 
these are the same for different SCR numbers; this is because the 
auxiliary equipment is different, thus necessitating a different SCR 
number. Receiving T. P. S. sets have been included because they 
can be used for low frequency amplification, although ground teleg¬ 
raphy itself is no longer used in army communications. 

It is the set boxes that are described in detail in this pamphlet. 
The following data will enable one to find the description desired: 

Set box BC-17 is the amplifier of the SCR-72 and SCR-147 sets. 

Set box BC-^4 is the amplifier of the SCR-72-B and SCR-148 sets. 

Set box BC-44-A is the amplifier of the SCR-121 and SCR-121-B 
sets. 

Set box BC-8-A is the amplifier of the SCR-144 set. 

Set box BC-101 is the amplifier of the SCR-149 set. 

Set box BC-103 is the amplifier of the SCR-145 set. 

Set box BC-104 is the heterodyne of the SCR-146 set. 

Full parts lists of each set are given in Section XI. 


Section II. 


NOTES ON CARE AND OPERATION OP AMPLIFIERS AND 

HETERODYNES. 


Paragraph. 


Care of apparatus- 2 

Care of telephones_ 3 


Operation of heterodynes- 

Operation of amplifiers_ 

Failure of amplifiers to operate- 

“ Howling ” of amplifier_ 

1 













2 


AMPLiriEES AND HETERODYNES. 


2 . Care of apparatus.—All radio apparatus, including amplifiers and 
heterod 3 mes, must be carefully handled. Eougli treatment will surely 
cause trouble by dislodging or loosening parts of the. apparatus, 
breaking electrical connections, either within the insulation or at the 
terminals, or, in the case of amplifiers, heterodynes, and other vacuum 
tube sets, breaking or changing the relative position of the elements 
of the tube. Therefore, it is necessary to handle radio apparatus with 
great care. Allowing the apparatus to become damp or wet will, in 
addition to causing rust and mold to form, nullify the insulating 
properties of the insulators used and in time destroy them. Radio 
apparatus should never be stored in a damp place. If unavoidably 
exposed to rain it should be carefully dried out by placing in a warm 
room, but never exposed to direct heat. 

3. Care of telephones.—The telephones furnished with the ampli¬ 
fiers are type P-11 head sets. These should never be taken apart, 
as they are ground after assembly to get the exact clearance between 
the diaphragm and the pole pieces. If it becomes necessary to change 
the plug or cord, these should be connected in the exact way the old 
ones were. The connections can be identified by the colored tracer 
threads running through the insulation of the wires. To test the 
connection, connect the tip of the plug to the positive lead of a 20-volt 
dry battery and the ring of the plug to the negative lead. Unscrew 
the caps from the receivers, remove the diaphragm, and test the 
strength of the magnet in each ear piece with it. The magnets in 
both ear pieces should be stronger than the plug is connected to the 
dry battery than when it is not. If not stronger, proper connections 
of the cords and plugs have not been made. 

4 . Operation of heterodynes.—^In operating a heterodyne there are 
two important factors to be considered. The one factor is the 
strength of the oscillation set up at the detector by the heterodyne. 
There is a definite though not critical strength, varying for different 
received signals, at which the reception is best. The strength of the 
oscillation set up at the detector by the heterodyne may be varied by 
changing the strength of the oscillations generated by the heterodyne 
or by changing the coupling between the heterod^me and the receiv¬ 
ing circuits. The strength of the oscillations generated by the hetero¬ 
dyne may be controlled to some degree by control handles, usually 
rheostats, placed on the heterodyne for this purpose. Changing the 
coupling between the heterodyne and the receiving circuits may be 
done by means of a coupling control handle for this purpose, as in 
the set box type BC-104. If no such control is provided the coupling 
may be changed by varying the relative position of the heterodyne 
and the receiving circuits. Increasing the distance increases the 
coupling. The coupling may be also changed by changing the angle 


AMPLIFIERS Ai!TD HETERODYNES. 


3 


between the coil of the heterodyne and the coil of the receivinjr set 
to which it is coupled. When the two coils are parallel the coupling 
is greatest; when at right angles the coupling is least. 

The other important factor in the operation of the heterodyne is 
the frequency of the oscillations. The difference between the fre¬ 
quency of the received oscillations and those generated by the hetero¬ 
dyne determines the pitch of the note heard in the receiver and must 
be equal to an audio frequency. As the frequency of the received 
oscillations is determined at the transmitting station, these can not 
be changed at the receiving station. The frequency of the hetero¬ 
dyne, however, is under control and is varied so as to produce the 
desired audio frequency. The heterodyne frequency is varied by 
changing either the capacity or inductance in the circuit or by 
changing both of these. A heterodyne has control handles for this 
purpose. The setting of these handles is very sensitive. Thus, if 
the control handles were moved from a setting that gives oscilla¬ 
tions whose wave lengths is 600 meters to a setting that gives oscilla¬ 
tions whose wave length is 605 meters, the difference in frequency of 
the two wave lengths would be 4,300. This change in frequency is 
enough to make the note pass from audibility to inaudibility. So 
delicate is the apparatus, especially for short wave lengths, that in 
many heterodynes the approach of the operator’s hand to the control 
handle gives capacity enough to change the note heard in the re¬ 
ceivers. The set box type BC-104 is shielded so as to avoid as far 
as possible any such outside influences. In turning the control 
handles of a heterodyne a click is sometimes heard in the telephones 
of the receiving set. This click occurs at the point where the hetero¬ 
dyne oscillations and the received oscillations have the same fre¬ 
quency. It is just to either side of this point that the signals can be 
heard. 

5 . Operation of amplifiers.—By means of the rheostats on the set 
boxes the degree of amplification can be controlled. Use the mini¬ 
mum amount of current that will give readable signals. Interference 
from other stations may sometimes be eliminated by adjusting the 
rheostats. Interchanging the vacuum tubes, even in an amplifier, 
may give better results. If a tube does not light up, clean its con¬ 
tact points and try it again. It may be that the tube is burned out. 
If so, it must be replaced by a new tube. If the filaments of vacuum 
tubes are connected in series, the burning out of one tube will prevent 
the others from lighting. The defective tube can be found by trial 
and be replaced. A good test for a low-frequency amplifier is to 
gently tap the first tube. If the amplifier is working properly, a 
ringing sound will be heard in the telephone receivers. 

6. Failure of amplifiers to operate.—Amplifiers may fail to operate 
even when the filament tubes are lighted. The trouble usually lies 

83564°—22-2 



4 


AMPLIFIERS AND HETERODYNES. 


in tlie high-volt battery. This should be examined for loose or 
broken connections, and should be tested as to voltage, which should 
not fall below 38 volts. A frequent cause of a high-volt battery run¬ 
ning down is the storage of these batteries in such a way that their 
terminals are short-circuited. Short-circuiting a high-volt dry bat¬ 
tery for only a few moments will make it worthless. High-volt bat¬ 
teries connected with wrong polarity will prevent the amplifiers from 
operating and hence should be checked up. If no trouble is found 
with the batteries, the other connections you have made should be 
checked up. If no faults are found, the trouble may be in a loose or 
broken connection within the set box. 

7. Howling^’ of amplifier.—Sometimes an amplifier “howls” or 
“sings.” This drowns out the signals. There are numerous causes 
for this howling. A loose, broken, or dirty connection of the high- 
potential battery will cause it, as will also leakage or local action 

in that battery. The remedy lies in correcting the fault in the 
connections or battery. Another source of howling lies in a defective 

vacuum tube which, to the eye, is apparently in good condition. Such 
a tube must be replaced. It can be found by trial. Allowing the 
leads from the filament battery, the high-volt battery or to the tele¬ 
phones to touch each other is liable to cause howling, especially if 
these leads are free to move or swing against each other. The most 
frequent cause of howling, however, is too great a filament current. 
This can be controlled by the rheostat, usually placed on the ampli¬ 
fier. If there is none on the amplifier, an outside one can be connected 
in series with the filament battery. If the fault is not located 
among the above, grounding the negative terminal of the filament 
battery will often prevent howling. Insulating the amplifier from 
the ground has been found helpful in some cases. Sometimes revers¬ 
ing the input connections will eliminate the howling. It must be re¬ 
membered that very often the foreign noises heard in the receivers 
of an amplifier are not caused by the amplifier but are due to other 
causes such as atmospherics, nearby electrical circuits or machinery, 
etc. 

Section III. 

AMPLIFIER SET BOX, TYPE BO-17 (Used in SCR-72 and SCR-147 sets). 

Paragraph. 


Purpose of amplifier- 8 

The amplifier set box- 9 

The interior of the set box- 10 

Installing the BC-17- 11 

Operating the BO-17- 12 


8. Purpose of amplifier.—This set box is an audio frequency ampli¬ 
fier using VT-1 tubes, giving two stages of amplification. There is 
no detector and therefore the receiving set with which it is used 
must be provided with one, or a separate one must be used. The 







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FIG. 1.—AMPLIFIER SET BOX, TYPE BC-17, IN ITS 
CARRYING CASE. 





AMPLIFIERS AND HETERODYNES. 


5 


amplifier may be used for radio signals after detection, or for ground 
telegraphy signals. The latter use, however, is now obsolete. It was 
designed mainly for that use, and together with batteries and acces¬ 
sory equipment, was called set T. P. S. receiving, type SCR-T2. 

9. The amplifier set box.—^The amplifier apparatus proper, together 
with the high-potential batteries, is contained in one box. This 
box measures lOJ by 6 by lOJ inches high and weighs 13 pounds. It 
is carried in a carrying case having compartments for accessories 
and spares. A view of the amplifier in its carrying case is shown in 
figure 1. The front of the amplifier contains windows through which 
the two vacuum tubes can be seen. There is also a panel which bears 
telephone jacks and binding posts or Fahnestock clips. There are 
six telephone jacks arranged in pairs, which are in parallel. The 
pair to the left is used when it is not desired to use any amplification. 
The next pair is used for one stage of amplification, and the third 
pair for both stages. Beneath each pair of telephone jacks are two 
terminals to which a telephone head set may be connected if it is not 
provided with a plug to fit the jacks. On the lower left of the panel 
are two pairs of terminals or Fahnestock clips, suitably marked, to 
which the input to the amplifier is connected. The left pair is for 
ground telegraphy; the other pair for radio. On the lower right side 
of the panel are the terminals or Fahnestock clips to which to con¬ 
nect the 4-volt storage battery used for lighting the filament of the 
tubes. 

10. The interior of the set box.—Access to the interior of the ampli¬ 
fier box is obtained by raising the cover of the box. On either side 
are compartments with Fahnestock clip terminals for candying the 
high-potential batteries. Between these compartments is a space for 
the vacuum tubes, whose sockets are mounted on a shelf cushioned 
from mechanical vibration by being supported on a sponge rubber. 
Beneath this shelf are the intertube transformers, which are of the 
heavy iron-clad type, and other pieces of small apparatus. 

11. Installing the BC-17.— {a) Connect the 4-volt storage battery 
leads to the terminals “ +4 volt—” being sure to observe the proper 
polarity. If using the cord and battery provided with the set, do 
not plug into the battery until it is desired to receive signals. If 
using separate wires do not attach to battery until it is desired to 
receive signals. 

{h) Open cover of the box and place a BA-2 battery in each com¬ 
partment, face up and negative wire (black) to the rear. Connect 
the terminals to the clips provided, observing the proper polarity 
as marked on the edge of the compartment. (The rear terminal clips 
on each compartment are negative.) 

((?) Place two VT-1 tubes in their sockets, 


G 


AMPLIFIERS AND HETERODYNES. 


{d) Connect the output of the radio receiving set to the terminals 
marked “ Eadio.” The polarity of the connection makes no difference 
in the working of the amplifier. (The output of a radio receiving 
set having a detector is where one would connect the telephone if 
no amplifier were being used.) 

{e) Plug in the phones—preferably in one of the right-hand pairs 
of jacks. Finish the connection to the storage battery and the set is 
ready for operation. 

12. Operating the BC-17.—There are no controls on the amplifier, 
sometimes better amplification can be obtained by interchanging the 
two tubes. If the amplifier “sings” or “howls” it can usually be 
stopped by grounding the negative terminal of the filament batter}^ 
When the amplifier is not in use, the filament battery should be dis¬ 
connected from the set. Disconnect at the battery rather than at the 
set box. 

Sectio::^ IV. 

AMPLIFIER SET BOXES TYPE BC-44 (used in SCR-72-B and SCR-148 
sets) and TYPE BC-44-A (used in SCR-121 and SCR-121-B sets). 

Paragraph. 


Purpose of amplifiers__ 13 

The amplifier set boxes_ 14 

The interior of the set boxes_ 15 

‘Installing the BC-44 or the BC—44r-A _ 16 

Operating the BC-44 or the BC-44-A_ 17 


13. Purpose of amplifiers.—The amplifiers, type BC-44 and BC-44-A, 
are two stage audio frequency amplifiers, using VT-1 tube,s. The 
BC-44 w^as designed to receive ground telegraphy signals as well as 
radio signals and has an extra terminal for this purpose. This is the 
onlv essential difference between the two set boxes. There is no 
detector in the amplifiers and hence an outside detector must be 
used in receiidng radio signals before they can be amplified by these 
sets. 

14. The amplifier set boxes.—All parts of the amplifier, except the 
4-volt storage batteries, are carried in one box, which is divided into 
two compartments. The compartment to the left is to be used for 
storing the telephones and other accessories when they are not in use. 
The other compartment is closed by a bakelite panel. A cover, which 
can be clamped on a rubber gasket, protects the front of the set box. 
The set box, with its cover on, measures 16 by by 10 inches high, 
and with its spare parts and accessories weighs approximately 24 
pounds. It is provided with a web carrying strap. Figure 2 shows a 
view of the BC-44 set box with its cover removed. The front panel of 
the set box bears terminals, marked “ -f-B Batt— ” for an external 40 
volt battery, terminals marked “-|-4 volt—” for the filament storage 
















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FIG. 2.—AMPLIFIER SET BOX, TYPE BC-44, FRONT VIEW. 



FIG. 3.—AMPLIFIER SET BOX, TYPE BC-44, INTERIOR VIEW 






















AMPLIFIERS AND HETERODYNES. 


7 


battery, and terminals underneath two jacks marked “Phones” to 
which telephones may be connected if they are not provided with 
plugs to fit the jacks. There are also input terminals mounted on the 
panel. In the BC-44 these are three terminals, marked “Amplifier ” 
and “ Grround telegraphy.” In the BC- 11 A there is only one pair 
of terminals, marked “Amplifier.” The panel also bears a clip under 
which the 4-volt battery leads may be fastened. A filament rheostat 
handle, marked “ Fil current,” is the only control on the amplifier. 

15. The interior of the set boxes.*—Access to the interior of the com¬ 
partment carrying the radio equipment comprising the amplifier is 
gained by unscrewing a knurled knob in each upper corner and pull¬ 
ing forward the panel, which is hinged at its lower edge. The radio 
equipment in use, including a case for holding the high-volt batteries, 
is all mounted on the rear of the panel. A view of the interior of the 
BC-44 set box, with the vacuum tubes and high-volt batteries in¬ 
stalled, is shown in figure 3. The transformers, which are of the 
iron-clad type, are mounted underneath the shelf carrying the vacuum 
tubes. The vacuum tubes are cushioned from jars by being mounted 
in sponge rubber. The small cylindrical objects with beaded insu¬ 
lated leads are resistances of the filament rheostat. Behind the ap¬ 
paratus mounted on the panel is a space containing suitable holders 
for the carrying of spare dry batteries, vacuum tubes, and resistances. 

16. Installing the BC-44 or the BC 4 4-A.— (a) Turn “Fil current” 
rheostat to the “ Off ” position. 

(d) Connect a 4-volt storage battery to the terminals marked 
“ -f- 4 volts —,” being sure to observe proper polarity. 

(c) Unscrew the knurled screw in each upper corner and’pull the 
panel forward. Place in the holder mounted on the rear of the panel 
two BA-2 batteries with their faces up. Fasten the terminals of 
each battery to the Fahnestock clips, being sure to observe proper 
polarity. It is to be noted that the inner two clips are both positive 
and the outer two both negative. The rear pair of clips is to be 
used for the rear batter}^, the front pair for the front battery. Make 
all connections tight and clean. 

(d) If the BA-2 batteries are not available, an external 40-volt 
battery should be connected to the terminals in the front of the panel 
marked “ -f- B Batt —.” Observe the proper polarity as marked 
on the panel. 

(e) Place a VT-1 tube in each of the two sockets, close and fasten 
the panel. 

(/) Connect the two terminals of the output of the detector to the 
two binding posts marked “Amplifier.” (The output terminals of 
the detector are where the telephones would be connected if no am¬ 
plifier were used.) 



8 


AMPLIFIERS AND HETERODYNES. 


(g) Plug in the telephones in the jack marked “ Phones” or con¬ 
nect each lead of the telephone to one of the terminals immediately 
below the j ack and the set is ready for operation. 

17. Operating the BC-44 or the BC-44r-A. —Turn the “ Fil current ” 
rheostat clockwise until the tubes burn a cherry red. There are no 
other controls on the amplifier. The receiving apparatus must be 
tuned and the detector adjusted in the usual manner. The amount 
of amplification can be controlled somewhat by the filament rheostat. 
Turning the handle of this rheostat to the right increases the amplifi¬ 
cation. It must be remembered that this increases the brilliancy of 
the tubes and shortens their life. If the amplifier howls the filament 
current should be reduced. If this does not eliminate the trouble, try 
grounding the negative terminal of the filament battery. 

Section V. 

AMPLIFIER SET BOX, TYPE BO-8-A (used in SCR-144 set). 

Paragraph. 


Purpose of amplifier_ 18 

The amplifier set box_ 19 

The interior of the set box_ 20 

Installing the BO-8-A- 21 

Operating the BC-8-A- 22 


18. Purpose of amplifier.—This set box is designed to amplify and 
detect damped wave signals. By the use of a separate heterodyne 
undamped waves may also be received and amplified. There are 
three stages of radio frequency amplification, followed by a detector 
tube and two stages of audio frequency amplification. Six VT-1 
tubes are used. The amplification is greatest for waves whose length 
is 1,000 meters, but satisfactory amplification is obtained over wave 
length ranges of from 750 to 1,500 meters. 

19. The amplifier set box.—^The amplifying apparatus, except the 
batteries and certain accessories, is mounted in a box which meas¬ 
ures 15J by 6 by 8J inches high and weighs 10 pounds. The front of 
the box, shown in figure 4, is a bakelite panel on which are mounted 
the terminals and control handles. Along the lower edge of the 
panel are two pairs of terminals, the left-hand pair, properly marked, 
being for the 4-volt filament storage battery; the other pair, also 
properly marked, being for the 40-volt plate battery. The two termi¬ 
nals along the right edge of the panel are the input terminals, the 
upper one being marked “ Grid ” and the lower one ‘‘ Fil,” There 
is a telephone jack, marked “ 6 tubes,” to plug in the telephone when 
it is desired to use the full amplification furnished by the set. Im¬ 
mediately below this is a telephone jack marked “5 tubes” for use 
when it is not desired to employ the second audio frequency amplify- 



















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FIG. 4. 


AMPLIFIER SET BOX, TYPE BC-8-A, FRONT VIEW. 



AMPLIFIER SET BOX, TYPE BC-8-A, INTERIOR VIEW 



















AMPLIFIERS AFTD HETERODYNES. 


9 


ing tube. The panel bears two control handles; the one to the left 
marked ‘‘Fil control” turns on and off the filament battery. The 
other control varies the current passing through the filaments of the 
high frequency amplifying tubes. It is marked “ Fil. Elieo H. F.” 

20. The interior of the set box.—Access to the interior of the set box 
is gained by raising the cover, which is hinged at the rear. A shelf, 
supported in sponge rubber pads, carries sockets for the six vacuum 
tubes. Viewing the box from the front, the three tubes to the right 
are used for radio frequency amplification; the fourth tube is used 
as a detector, and the remaining tubes for audio frequency amplifica¬ 
tion. A view of the interior of the set box is shown in figure 5. The 
radio frequency and the audio frequency transformers are mounted 
below the shelf. The filament resistance for each tube appears in 
front of the tube sockets. The narrow tube between the third and 
fourth vacuum tube is the grid leak resistance. It is to be noted that 
the whole apparatus is carried on the front panel. 

21. Installing the BC-8-A.— (a) Place “ Fil. control ” switch to the 
“ Off ” position. 

(b) Connect a 4-volt storage battery to the binding posts marked 
‘‘ +Fil Bat—, 4 V.” Observe the correct polarity as marked. 

(e) Connect two 20-volt batteries (BA-2 or BA-8) in series to the 
binding posts marked “ -|-Plate Bat—, 40 Y.” It is very important 
that all connections be clean and tight and that the proper polarity 
is observed. 

(d) Place six VT-1 tubes in their sockets, which are made ac¬ 
cessible by opening the lid of the box. It may be found later that 
interchanging the tubes will give better results. Certain tubes are 
better amplifiers or detectors than others. This can be determined 
by trial. 

(e) Connect the two terminals of the output of the receiving set 
to the two terminals on the right of the set box marked “ Grid ” and 
“Fil.” If the radio receiving set has one side grounded, this side 
should be connected to the “ Fil ” binding post. If it is not known 
whether or not the receiving set has one side grounded, the proper 
connection can be found by trial. Use that connection which gives 
the best results. It is to be noted that this set box can be used only 
when the radio receiving set has no detector. 

(/) Insert the telephone plug into whichever jack it is desired to 
use and the set is ready for operation. 

22. Operating the BC-8-A. —Turn the “ Fil Eheo H.F.” control 
handle to the “Min” position. Turn the “Fil control” handle to 
the “ On ” position. Now turn the “ Fil Rheo H. F.” handle clock¬ 
wise until the filaments of the three tubes to the right become a 
cherry red in color. The radio receiving set should be tuned in the 


10 


AMPLIFIERS AND HETERODYNES. 


regular manner. Control of the amount of amplification is secured 
by the operation of the “ Fil Rheo H. F.” handle. In general this 
should be as close to the “ Min ” position as is possible, while main¬ 
taining signals of suitable strength. If there is a tendency for the 
amplifier to howl, the filament current must be reduced. Howling is 
more frequent when using the six tubes than when using only the 
five tubes. 

Section VI. 

AMPLIFIER SET BOX, TYPE BC-101 (used in SCR-149 set). 

Paragraph. 


Purpose of amplifier_ 23 

The amplifier set box_ 24 

The interior of the set box_ 25 

Installing the BC-101—using VT-S tubes_ 26 

Installing the BC-101—using VT-1 tubes_ 27 

Installing the BC-101—using a reactance coil_ 28 

Operating the BC-101_ 29 


23. Purpose of amplifier.—The amplifier, type BC-101, is a vacuum 
tube amplifier, using either three VT-1 or three VT-5 tubes. There 
are two stages of audio frequency amplification in addition to a de¬ 
tector tube. A switch is provided to use the detector tube together 
with the amplifier tubes or to use the amplifier tubes alone. Thus 
the amplifier can be used with a receiving set that contains a de¬ 
tector or with one that does not contain a detector. As only audio 
frequencies are amplified, this apparatus, like all other audio fre¬ 
quency amplifiers, is independent of the wave length of the radio 
signals. 

24. The amplifier set box.— The whole apparatus, except the storage 
batteries and certain accessories, is mounted in a box constructed of 
an aluminum frame which supports bakelite panels. The box is 
inches by 6J inches by 10 inches high and weighs 10|^ pounds. The 
terminals and controls are all mounted so as to be nearly flush with 
the projecting sides of the box. The binding posts are all mounted 
on these extended sides; the two to the left marked “ Grid ” and 
“ Fil ” being the input terminals. At the bottom to the left are the 
terminals for the filament battery marked “Fil Bat 4 V or 2 V,— 
and + ”; to the right of these are terminals for the 40-volt plate 
battery marked “ Plate Bat, — and +.” On the left are two termi¬ 
nals connected together by a copper strip which is removable. 
These terminals are for the insertion of a reactance coil when one is 
desired and are marked “ Tickler.” The front panel carries a double 
throw switch, one position of which, marked “ Detector,” throws the 
detector tube and the two amplifier tubes in circuit; the other po¬ 
sition, marked “Amplifier,” throws only the two amplifier tubes in 
circuit. To the right of this switch is a rheostat marked “ Fil con- 












riG.6. 


AMPLIFIER SET BOX, TYPE BC-101, FRONT VIEW 






















AMPLIFIER SET BOX. TYPE BC-IOl, INTERIOR VIEW. 














AMPUFIEES AND HETERODYNES. 


11 


trol detector” for controlling the filament current of the detector 
tube. To the right of this is another rheostat marked ‘‘Fil control 
amplifier ” for controlling the filament current of the two amplifier 
tubes. There are also two telephone jacks, in parallel, so that two 
pairs of telephone receivers can be plugged in. The upper part of 
the front panel is a door, having three small windows. The door 
permits access to the interior of the set for putting in the vacuum 
tubes. Figure 6 shows a view of the set box with this door open. 

25. The interior of the set box.—The aluminum frame of the box car¬ 
ries brackets which support a shelf mounted between sponge rubber 
pads to absorb mechanical vibration. This shelf carries the vacuum^ 
tube sockets and attached to the underside of it are the transformers 
and various small pieces of apparatus. The lower half of the back 
of the set box is a door which has mounted on it a frame having 
terminals for the two BA~2 batteries used in the set. Connections 
of these batteries are completed inside the box by spring clips- 
which engage when the door is closed. A view of the set box from 
the rear, with the upper panel removed and with the door open is 
shown in figure 7. It is to be noted that the BA-2 batteries are in 
place in their holders. The back of the vacuum-tube sockets are seen 
in the upper part of the view. The two audio frequency transformers 
can also be distinguished. Mounted on the inside of the right panel as 
viewed from the rear are supports which carry adapters (type FT- 
65) when these are not in use. Those adapters are to fit in the 
vacuum-tube sockets when VT-5 tubes are used. They can not be 
seen in the illustration. 

26. Installing the BC-101—using VT-5 tubes.— {a) Turn ‘‘ Fil control 
detector” counterclockwise to the “ Off ” position. Do same to the 
“ Fil control amplifier.” 

{h) Connect a 2-volt storage battery or a closed circuit (ignition 
type) dry cell to binding post marked “ Fil Bat, 4 V or 2 V.” Be 
sure to observe correct polarity as marked on the set box. 

(c) Open rear door and place in the holder mounted thereon two 
type BA‘-2 dry batteries. Place these batteries face up with their 
positive terminals (red wires) next to the door. Fasten the batteries 
in the holder by means of the copper strip spring provided, spread¬ 
ing the wires apart so that there are no wires between the spring and 
the face of the batteries. Obeying the following rule: ‘‘Do not 
connect the terminals from the same BA~-% battery to the two termi¬ 
nals on the holder whieh are connected by a copyer stripf'‘ connect 
the four terminals of the two batteries to the four terminals pro¬ 
vided on the holder, observing the proper polarity. Be sure to have 
all connections clean and tight. Press all the wires down so,that 
they lie close to the batteries. After removing the adapters from 
their holders inside the box, close the door. 

83564°—22-3 



12 


AMPLIFIERS AND HETERODYNES. 


{d) If BA-2 batteries are not available a 40-Yolt battery must be 
connected to the terminals on the front of the box marked “ Plate 
Bat 40 V.” Be sure to observe correct polarity as marked, in the 
set box. 

{e) Open the door on the front panel and place an adapter in each 
vacuum-tube socket. Place VT-5 tubes in the adapters and close the 
door. It may be found later that interchanging the tubes will give 
better results. Certain tubes are better amplifiers or detectors than 
others. This can be determined by trial. 

(/) Connect the two terminals of the output of the radio receiving 
set to the two terminals marked “Input, grid and fil ” on the left of 
the amplifier. If the radio receiving set has one side grounded, this 
grounded side should be connected to the “ Fil ” terminal. If it is 
uncertain whether or not the radio receiving set is grounded, the 
proper connection can be found by trial. The connection which gives 
the best resulting signal should I e used. 

{g) Throw the double switch down to the “Amplifier” position 
if the receiving set has a detector that is being used; otherwise 
throw the double-throw switch up to the “ Detector ” position. Plug 
in the phones and the amplifier is now ready for operation. 

27. Installing the BC-101 —using VT-1 tubes.— [a) Follow directions 
given in subparagraph {a) of paragraph 26. 

(h) Connect a 4-volt storage battery to the binding posts marked 
“ Fil Bat, 4 V or 2 V.” Be sure to observe correct polarity as 
marked in the set box. 

{c) Follow directions of paragraph 26 (c?) to 26 (^), inclusive, 
except that the adapters are not to be used. 

28. Installing the BC-101 —using a reactance coil.— {a) Follow direc¬ 
tions either of paragraph 26 or 27, according to the type of vacuum 
tube to be used. The tickler terminals should be connected to the 
“tickler” or “feed back” or “reactance coil” in the receiving set, 
if there be any, when it is desired to receive undamped wave signals. 
It may be found necessary to reverse the connections to the amplifier 
tickler terminals to get the proper coupling. This can be deter¬ 
mined by trial. When using a tickler the short-circuit strip between 
the two terminals on the amplifier should be disconnected at the 
upper terminals. 

{h) If the receiving set has no tickler coil and there is no other 
method of receiving undamped waves, a method using this amplifier 
can be devised. The necessary conditions are that an inductance 
of the proper value connected to the tickler terminals be inductively 
coupled to the secondary receiving inductance of the receiving set. 
The amount of inductance to be used will vary with the type of 
receiving set, and also to some degree with the wave length of the 
incoming signals. The inductance to be used and its position may be 


AMPLIFIERS AND HETERODYNES. 


13 


found by trial. Start by winding No. 24 silk-covered magnet wire 
in a single layer on a cylinder about 4 inches in diameter, leaving 
fairly long leads. The turns should be close together and there 
should be enough turns to make the coil about 1 inch wide. Attach 
the leads to the tickler terminals and place the coil near to and 
parallel with the secondary receiving inductance. If no results are 
obtained, turn over the coil you have made. If success is still lack¬ 
ing, try the coils in various positions with respect to the secondary 
receiving inductance, inverting the coil in each position. If still un¬ 
successful, change the number of turns on the coil and try again. 

29. Operating the BC-101.— (a). Turn the “Fil control amplifier” 
switch clockwise until the two tubes to the right show a cherry red. 
If the detector tube is being used, do the same with the “ Fil control 
detector.” However, if the amplifying tubes only are used the 
detector tube is out of circuit and will not light up. 

(h) Tune the receiving set in the usual method. 

(c) Adjust the detector and amplifier tubes by means of their 
filament controls to give the most readable signals. It must be 
remembered, however, that burning the tubes too brightly greatly 
shortens their lives. 

(d) If the amplifier howls or sings, try decreasing the brightness 
of the tubes, especially the amplifier tubes. 

(e) When the amplifier is not in use, turn both filament-control 
switches counterclockwise to the “ Off ” position. 

Caution.—If the BC-101 is used with other tube sets it should be 
furnished loith a separate filament battery., otherwise the plate bat¬ 
tery of the other set may be short-circuited. 

Section VII. 

AMPLIFIER SET BOX TYPE BC-103 (used in SCR-145 set). 

Paragraph. 


Purpose of amplifier- 30 

The amplifier set box- 31 

The interior of the set box- 32 

Installing the BC-103- 33 

Operating the BO-103- 34 


30. Purpose of amplifier.—The amplifier, type BC-103, is designed to 
amplify, or detect and amplify, radio signals whose wave lengths 
are from 1,000 to 3,000 meters. It will amplify signals of other wave 
lengths, but the best amplification is produced within the above 
range. There are provisions made for three stages of radio frequency 
amplification, followed by detection, and two stages of audio fre¬ 
quency amplification. There are provisions made also for the use of 
the two audio frequency stages only. The amplification given by 
the latter is independent of the radio wave length of the signal. 
Six VT-1 tubes are used in the amplifier. 







14 


AMPLIFIEES A]^D HETERODYNES. 


31. The amplifier set box.—The whole apparatus, except the bat¬ 
teries and certain accessories, is contained in a set box whose dimen¬ 
sions are 15| by 6 by 8J inches high, and whose weight is approxi¬ 
mately 10 pounds. The front of the box is shown in figure 8. There 
are terminals to which to connect the plate and filament batteries, 
and also two sets of terminals to which to connect the out^^ut of a 
radio receiving set. The terminals to the right marked ‘‘ Grid” and 
“ Fil” are to be used when the radio receiving set has no detector, or 
one which is not in use. The terminals at the lower center are to be 
used when the radio receiving set has a detector that is being used. 
In addition to these terminals the panel carries a filament control 
switch for turning off and on the current in the filament; a filament 
rheostat that controls the amount of current in the high frequency 
amplifying tubes; a two-way switch that must be thrown to the 
proper position when the amplifier is used for either of its two pur¬ 
poses; and an amplification switch which controls the amount of 
amplification produced by the high frequency amplifying tubes. 
There are two telephone jacks on the left of the panel. The lower 
one marked “ 5 tubes,” uses only one stage of audio amplification; the 
upper one marked ‘‘ 6 tubes,” uses both stages. All terminals and 
control switches are appropriately marked. 

32. The interior of the set box.—The top of the set box is hinged 
so as to permit access to the six tube sockets. These sockets are for 
the VT-l tubes used in the set and are mounted on a shelf. The 
three tubes to the right are the radio frequency amplifiers, the fourth 
tube from the right is the detector; the other tubes are audio fre¬ 
quency amplifiers. Mounted on the lower side of the tube shelf are 
transformers and other pieces of equipment. The tube shelf is cush¬ 
ioned against jars and vibration by sponge rubber, and is supported 
by brackets attached to the bakelite panel. Access to the apparatus 
for repairs can be had by removing the panel, which is held in place 
by machine screws. Fig. 9 shows how the apparatus is mounted on 
the back of the panel. In the figure, three radio frequency trans¬ 
formers are seen at the lower left and two audio frequency trans¬ 
formers at the lower right. The narrow tube between these two sets 
of transformers is the grid leak resistance. 

33. Installing the BC-103.— {a) Place “ Fil control ” switch on ‘‘Oft’” 
position. 

{h) Connect a 4-volt storage battery to the binding posts marked 
“ 4 Y.” Be sure to observe the correct polarity as marked on the set 
box panel. 

{c) Connect two 20-volt batteries (BA-2 or BA-8) in series to the 
binding posts marked ‘‘ 40 Y.” Be sure to observe the correct polarity. 
It is especially important that all connections of these batteries be 
clean and tight. 



AMPLIFIER SET BOX, TYPE BC-103, FRONT VIEW. 



AMPLIFIER SET BOX, TYPE BC-103, INTERIOR VIEW. 















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AMPLIFIERS AND HETERODYNES. 


15 


{d) Place six VT-1 tubes in the sockets which are made accessible 
by opening the lid of the box. It may be found later that inter¬ 
changing the tubes will give better results. Certain tubes are better 
amplifiers or detectors than others. This can be determined by trial. 

(e) For audio frequency amplification {used when the radio receiv¬ 
ing set has a detector 'which is in use)^ —Connect the two terminals 
of the output of the radio receiving set to the two terminals on the 
lower center of the box marked “Audio amplification.” The polarity 
of the connection makes no difference in the working of the amplifier. 
(The output terminals of the radio receiving set are at the jack or 
binding posts to which the telephones would be connected if no 
amplifier were being used.) 

Throw the double throw switch in the upper center of the panel 
doum^ to the position marked “Audio.” 

(/) For radio freq'uency amplifcation {used when the radio re¬ 
ceiving set has no detector or one that is 7iot in use ).—Connect the 
two terminals of the output of the radio receiver to the two terminals 
on the right of the amplifier marked “Input,” one being labeled 
“ Fil ” and the other “ Grid.” If the radio receiving set has one 
side grounded, this grounded side should be connected to the “ Fil ” 
terminal. If it is uncertain whether or not the radio receiving set 
is grounded, the proper connection can be found by trial. The con¬ 
nection which gives the best resulting signals should be used. 

Throw the double throw switch in the upper center of the panel 
up to the position marked “ Kadio.” 

{g) Insert the telephone plug into whichever of the jacks marked 
“ 5 tubes ” or “ 6 tubes ” it is desired to use. The amplifier is now 
ready to use. 

34. Operating the BC-103.— {a) For audio frequency amplification .— 
There is only one control switch, the “ Fil control ” switch. When it 
is desired to receive signals this should be turned to the “ On ” posi¬ 
tion. The two vacuum tubes should light up. Nothing more need 
be done to the amplifier. 

(&) For high frequency amplification. —There are three controls 
for the operation. The “ Fil control ” switch is thrown to the “ On ” 
position which causes all the tubes to light up. The other controls 
marked “ Fil rheo H. F.” and “Amplification ” are for controlling the 
amount of amplification of the tubes. In general the “ Fil rheo 
H. F.” should be adjusted so that the high frequency amplifying 
tubes show the same brilliancy as the low frequency tubes. The de¬ 
gree of amplification can still further be controlled by turning the 
“Amplification ” switch—turning in a clockwise direction gives 
greater amplification. If this switch does not give as great a con¬ 
trol of the amplification as desired, the “Fil rheo H. F.” may be 
used. Increasing the brilliancy of the tubes by this switch increases 
83564°—22-4 



16 


AMPLIFIERS AND HETERODYNES. 


the degree of amplification; decreasing the brilliancy decreases the 
amplification. In some cases the amplifier will ‘‘sing” or “howl,” 
due to oscillations being set up in it. Such “ singing ” or “ howling ” 
prevents the reading of the signals. If they occur they can usually 
be stopped by moving the “ Fil rheo H. F.” switch one or two con¬ 
tacts toward “ Min ” and decreasing the degree of amplification by 
means of the “Amplification switch.” Sometimes in addition to the 
above it is necessary to turn the “ Fil control ” to the “ Off ” position 
for an instant before the “howling” or “singing” will disappear. 
Howling is more frequent when using the six tubes than when using 
only the five tubes. 

Section VIII. 

HETERODYNE SET BOX TYPE BC-104 (used in SCR-146 set). 

Paragraph. 


Purpose of the heterodyne_ 35 

The heterodyne set box_ 36 

The interior of the set box_ 37 

Installing the BC-104_ 38 

Operating the BS-104; receiving set calibrated—wave length known_ 39 

Operating the BC-104; re.ceiving set not calibrated—wave length known. 40 

Operating the BC-104; receiving set calibrated—wave length unknown_ 41 

Operating the BC-104; receiving set not calibrated—wave length 

unknown_ 42 


35. Purpose of the heterodyne.—The heterodyne, type BC-104, is a 
VT-1 oscillator designed to set up weak oscillations over a frequency 
range corresponding to wave lengths of between 800 and 3,400 meters. 
These weak oscillations are used in the reception of undamped waves 
of the same range of wave length by the heterodyne method. The 
heterodyne may be used as a wavemeter. (See Radio Communica¬ 
tion Pamphlet No. 28.) It must be remembered that, when used for 
this purpose, the results may not be so strictly accurate as if obtained 
by an instrument designed primarily as a wavemeter. 

36. The heterodyne set box.—The whole apparatus, except the bat¬ 
teries and certain accessories, is mounted in a box which measures 
8 by 9 b}^ 11^ inches high and weighs 12 pounds. The front of this 
box is shown in figure 10. On the lower edge of the front panel are 
binding posts for connecting the batteries, the pair to the left being 
for the 4-volt battery; the pair to the right for the 40-volt battery. 
In the upper left corner is a binding post for the antenna lead in 
wire, and in the upper right a binding post for connecting to the 
receiving set used. There is a “ Fil control ” switch for turning on 
and off the filament current; a “ Coupling ” control handle for vary¬ 
ing the coupling between the circuits of the oscillator proper and 
the circuit which is a part of the antenna lead in wire. A double 
throw switch to the left controls the amount of inductance in the 
oscillating circuits, thus enabling the variable air condenser to have 








FIG. 10. 


HETERODYNE SET BOX, TYPE BC-104, FRONT VIEW 





















HETERODYNE SET BOX. TYPE BC-104, INTERIOR VIEW 

















AMPLIFIERS AND HETERODYNES. 


17 


two ranges of wave length. The variable air condenser gives wave 
lengths of from 800 to 2,000 when the double throw switch is thrown 
down to the “ Short-wave ” position, and gives wave lengths of from 
1,400 to 3,400 when the double throw switch is thrown up in the 
“Long-wave” position. The reading on the scale of the variable 
condenser should be multiplied by 100 to give the wave length. The 
air condenser is controlled for coarse adjustments by a large knob. 
For fine adjustments it is controlled by a small knob placed at the 
lower right of the large knob. When using the coarse-adjustment 
knob the smaller knob should have its gears disengaged. This is 
done by pulling the smaller knob slightly outward. 

37. The interior of the set box.—^The whole apparatus is mounted on 
the front panel of the box, which is lined throughout with copper 
to prevent any electrical field set up by the oscillator from being 
picked up by the antenna or other receiving apparatus. The vari¬ 
able air condenser is thoroughly shielded also so as to reduce to a 
minimum outside influences affecting the frequency of the oscilla¬ 
tions. A view of the interior of the set box is shown in figure 11. 
On the large coil at the upper left is wound both the plate and the 
grid inductances, the latter having two taps. The small coil below 
contains the antenna inductance and rotates around a horizontal 
axis so as to provide different degrees of coupling with the coil 
above. The vacuum tube is mounted on a shelf supported by sponge 
rubber held in brackets on either side. The shelf also carries the 
filament resistance. The condenser shown at the right of the tube 
is the high-frequency by-pass condenser shunted across the 40-volt 
battery terminals. Below this condenser is a switch which is so de¬ 
signed that it has no appreciable electrical capacity. The large vari¬ 
able air condenser appears at the bottom of the illustration. 

38. Installing the BC-104.—(a) Throw the “ Fil control ” switch to 

the “ Off” position. 

{h) Connect a 4-volt storage battery to the terminals marked 
“ 4 V,” being sure to observe the proper polarity. 

{c) Connect a 40-volt battery (two type BA-2 or two type BA-8 
in series) to the terminals marked “40 volts.” Be sure to have all 
connections tight and clean as well as observing the proper polarity. 

{d) Baise the lid of the box and put a YT-1 tube in its socket. 

{e) Connect the antenna lead-in wire to the binding post marked 
“ Ant.” 

(/) Connect the binding post of the heterodyne marked “Bee’ 
to the binding post of the receiving set marked “ Ant or other simi¬ 
lar designation. 

{g) Turn the “Fil control” to the “On” position and the set is 
ready for operation. 

39. Operating the BC-104j receiving set calibrated ^wave length 
known.— {a) Tune the receiving set to the wave length to be received. 


18 


AMPLIFIERS AND HETERODYNES. 


(d) Place the double throw switch of the heterodyne either in the 
long wave or short wave position, depending upon-the wave length 
to be received. 

(e) Turn the “Coupling” handle until the pointer shows a cou¬ 
pling of 20 degrees. 

(d) Pull outward the small fine adjustment knob of the variable 
condenser. 

(e) Set the pointer of the variable condenser on the wave length 
to be received, using the large knob. 

(/) Press in the fine adjustment knob so that its gears are meshed 
and turn slowly back and forth until the note is heard in the tele¬ 
phones and is of the proper pitch. 

{g) Readjust the “ Coupling” until the note heard in the tele¬ 
phones is of the proper intensity. The fact that the receiving set 
also needs final adjustment must not be overlooked. 

40. Operating the BC-104; receiving set not calibrated—wave length 
known.— {a) Place the double throw switch of the heterodyne either 
in the long wave or short wave position, depending upon the wave 
length to be received. 

(&) Turn the coupling handle until the pointer shows a coupling 
of 20 degrees. 

(c) Pull outward the small fine adjustment Imob of the variable 
condenser. 

(d) Set the pointer of the variable condenser on the wave length 
to be received, using the large knob. 

(e) Press in the small fine adjustment Imob until the gears mesh. 

(/) Put the secondary of the receiver on aperiodic if it has this 

arrangement. 

(g) Adjust the coupling control in the receiver to give the maxi¬ 
mum coupling. 

(h) Vary the tuning of the primary of the receiver (and sec¬ 
ondary also if there is no periodic arrangement) and at the same 
time turn the fine adjustment knob of the heterodyne slowly back 
and forth. It is not necessary to move the knob more than a third 
of a turn either side of its first position. 

(i) After the signal has been picked up make final adjustments. 

41. Operating the BC-104; receiving set calibrated—wave length un¬ 
known.— (a) Place the double-throw switch of the heterodyne in 
short-wave position. 

(h) Turn the coupling handle until pointer shows a coupling 
of 20°. 

(c) Pull outward the small fine adjustment. 

(d) Set the pointer of the variable condenser on the shortest marked 
wave length. 


AMPLIFIERS AND HETERODYNES. 


19 


(e) Press in the fine-adjustment knob until the gears mesh. 

(/) Tune the receiving set to the wave length to which the heter¬ 
odyne has been set, using a close coupling. 

(gf) Turn the fine-adjustment knob of the heterodyne slightly back 
and forth, not moving it more than a third of a turn from its original 
position. 

(h) If the signal is not picked up, turn the variable air condenser 
of the heterodyne to the next lowest wave length and repeat as above. 

42. Operating the BC-104; receiving set not calibrated—wave length un¬ 
known.—This is a difficult task and requires much patience. It can be 
done by placing a variable condenser of the heterodyne on a definite 
wave length and tuning the primary and secondary of the receiving 
set. The receiving set should have the closest possible coupling be¬ 
tween its primary and secondary. If there is an arrangement for 
making the secondary aperiodic, this should be done. The broadest 
Idnd of tuning should be used until the signal is picked up. The fine- 
adjustment knob of the heterodyne should be turned slightly back and 
forth with each setting of the receiver tuning elements. If the signals 
are not picked up, the heterodyne should be placed on another wave 
length and the process repeated. In order to receive the signal it is 
necessary that the frequency of the primary of the receiver, the 
secondary of the receiver, and the heterodyne be approximately the 
same. These conditions can be brought about by trial as described 
above. 

Section IX. 

PRINCIPLES OF AMPLIFIERS. 

Paragraph. 


Definition of amplification constant- 43 

Value of amplification constant_ 44 

Operating conditions for amplification- 45 

Limit and control of amplification- 40 

Low frequency amplifiers- 47 

Comparison of the low frequency and high frequency amplifier_ 48 


43. Definition of amplification constant.—A vacuum tube can be used 
as an amplifier because, under correct conditions, a voltage applied 
to the grid has a greater effect upon the plate current than the same 
voltage applied to the plate. This may be expressed more accurately 
as follows: A change in the grid potential produces [jl' times as 
great a change in the plate current as an equal change in the plate 
voltage. The quantity, [jl', is called the amplification constant of 
the tube, and is the maximum voltage amplification that can be 
obtained from the tube. Mathematically [)/ can be expressed as 

^ = — /x' where ep and eg are respectively the plate and grid potentials. 








20 


AMPLIFIERS AND HETERODYNES. 


44. Value of amplification constant.—The amplification constant de¬ 
pends upon the structure and geometry of the tube. The mesh of 

the grid, the diameter of the grid wires, the distance between grid 
and plate, and between grid and filament are the more important 
factors which determine the value of this constant. The value of [j/ 
may vary under extreme conditions of voltages applied to the tube 
but for ordinary operating ranges it may be considered as an un¬ 
changing value. [J.' equals 6.5, very nearly, in the VT-1 tubes used 
in Signal Corps amplifiers. 

45. Operating conditions for amplification.—In order to secure ampli¬ 
fication certain conditions must be obtained. The filament must be 
hot enough to emit enough electrons so that the plate current is not 
limited by the number of electrons available. The plate voltage 
must be high enough to establish a strong electric field within the 
tube. The potential of the grid should at all times be sufficiently 
negative so that it will not absorb appreciable current and thus dis¬ 
tort the gidd voltage-plate current characteristic of the tube. The 
average potential of the grid with respect to the filament is desig- 

. nated by the term “ biasing potential.” In addition, for distortion¬ 
less amplification, the voltage applied to the plate should be of such 
a value as to keep the dynamic characteristic of the tube as near a 
straight line as is possible with the external circuits used. The high 
impedance generally used in the plate circuit produces this condition. 

46. Limit and control of amplification.—It has been shown (Ther¬ 
mionic Vacuum Tube, Van der Bij 1) that the voltage amplification 
of a tube as available across an external resistance is in the plate 
circuit expressed by; 

M 

1 I 

where and are respectively the internal plate resistance of the 
tube and the external resistance, and where and are the effective 
alternating voltages of the plate and grid. An inspection of this 

equation shows that the ratio — will increase with a decrecme of 

the plate resistance and will also increase with an increase of the 

R 

external resistance. If the external resistance becomes infinite, 

becomes zero, and the right-hand number of the equation becomes — 
This means that the voltage amplification produced by a tube is lim¬ 
ited to the amplification constant of the tube. The plate resistance 
of the tube depends mainly upon the geometry of the tube, but also 
depends upon the filament emission and average grid potential. 
The filament emission is changed with a change in temperature of 
the filament, and hence it is seen that an amplification produced by 




AMPLIFIERS AFTD HETERODYNES. 


21 


a tube can be controlled to some degree by a rheostat placed in its 
filament circuit. 

47. Low frequency amplifiers.—It is standard practice to have the 
output of one low frequency amplifier tube pass through the primary 
of a transformer, the secondary of which is connected to the grid 
and filament of the next tube. In this manner advantage is taken 
of the step up in voltage produced by the transformer as well as 
the amplification produced by the first tube. It can be shown that 
with an ideal transformer in which the coupling is tight and the load 
circuit is resistive only, the ratio of grid voltage between successive 
tubes is expressed by the following equation: 


^g2_ 

^gl 


ju'n 


n^ + 


-^g2 

'^Pl 

X. 


where ^g 2 =effective alternating voltage on grid of 2nd tube. 
^gi=effective alternating voltage on grid of first tube. 

amplifying constant of 1st tube. 

7ir=:ratio of secondary to primary voltage in transformer, 
alternating current grid-filament resistance of 2nd tube, 
alternating current plate-filament resistance of 1st tube. 


It 

An inspection of this equation shows that if becomes infinite, 

the ratio of grid voltage becomes equal to which is the maxi¬ 
mum possible value. The plate resistance of the tube is inherent in 
the design of the tube and can not be made equal to zero, but the 
grid resistance of the second tube can be made very large by placing 
the right biasing potential on it, although it can not be made infinite 
because of the residual gas in the tube and surface leakage in con¬ 


nections. 


If the finite ratio 


R 


g2 


R 


PI 


and the amplification constant, [j.', 


are kept constant, it may be shown by plotting that is a maxi- 


R 


mum when Substituting this ideal value of n in the basic 

equation, it is found that the maximum amplification, i. e. — 


becomes equal to ^ [x'w. 

The above discussion is based upon an ideal transformer and takes 
no account of the no-load reactance, the leakage induction, and the 
core losses met with in a real transformer. 

The effect of these is to reduce the value of the voltage ratio at¬ 
tainable. Considering only the no-load reactance of the transformer 
(the other quantities can be made small) it can be shown that the 
best ratio of transformation, ti, is 4 or 5 to 1, that the ratio of grid 
voltages increases with an increase of the grid-filament resistance of 









22 


AMPLIFIEES AND HETERODYNES. 


the second tube, that the ratio of grid voltages is not the same for all 
frequencies, and that the latter depends mainly upon the no-load re¬ 
actance of the transformer primary. The effect of frequency upon 
the amplifying power of the tube is shown in figure 12, taken from 
“ Principles of Eadio Communication ” (Morecroft) and upon which 
this presentation is based. The curves of the figure show the theo¬ 
retical relation between the ratio of the potentials of two successive 

grids and the frequency. The plate-filament alternating current re¬ 
sistance is equal to 10,000 ohms; jJ'*' equals 6, and n equals 4. In 

curves A, B, and C the grid-filament alternating current resistance 



is equal to 250,000 ohms; the no-load inductance of the repeating 
transformer primary is equal to 2 henries in curve A, to 5 henries in 
curve B, and to 10 henries in curve C. In curves D, E, and F the 
grid-filament alternating current resistance is equal to 1,000,000 
ohms; the no-load inductance of the repeating transformer primary 
is equal to 2 henries in curve D, to 5 henries in curve E, and to 10 
henries in curve F. 

If the amplifier is used in radio telephony it is important that the 
amplification be the same for all frequencies, otherwise speech dis¬ 
tortion would result. The conditions upon which this can be ob¬ 
tained may be seen in the figure. 















































































AMPLIFIERS AND HETERODYNES. 


23 


• 48. Comparison of low frequency and high frequency amplifier.—Be¬ 
cause of the small effect at low frequencies it is unnecessary to take 
into account many phenomena that become important at high fre¬ 
quencies, and hence the designing of a low frequency amplifier is a 
much simpler task than that of a high frequency amplifier. With 
high frequency the small capacity of the tube and its leads become 
of prime importance. It is standard practice in the Signal Corps 
to use iron core intervalve transformers between high frequency 
amplifying tubes as well as between low frequency amplifying tubes. 
The iron core of the transformer adds to the difficulty of calculating 
the electrical constants. A high frequency transformer works best 
over a certain range of wave lengths if it possesses high efficienc}^ 



Section X. 


PRINCIPLES EMBODIED IN THE SET BOXES AND THEIR CIRCUIT 


DIAGRAMS. 

Paragraph. 


Amplifier set box, type BC-17- 49 

Amplifier set boxes, types BO-44 and BC-44-A- 50 

Amplifier set box, type BC-8-A- 51 

Amplifier set box, type BC-101- 52 

Amplifier set box, type BO-103- 53 

Heterodyne set box, type BC-104- 54 


49. Amplifier Set Box Type BC-17.—This amplifier is a low frequency 
amplifier using iron core transformers. The circuit diagram is shown 
in figure 13. It is to be noted that connections are provided for tele- 






























































24 


AMPLIFIERS AND HETERODYNES. 


phones so as to use one, two, or no stages of amplification. The plate 
voltage is 20 volts, there being one battery for each tube. The fila¬ 
ments are connected in parallel and no filament rheostat is provided. 
The grid is connected to the negative side of the filament. The drop 
in potential through the secondary of the transformers is sufficient 
to keep the grid at the negative potential that insures good operation. 
There are four input terminals arranged in two pairs. One pair 
uses the whole of the primary of the transformer, while the other 
pair uses only a part of it. Certain vacuum tubes require a greater 
filament voltage than others. In these tubes the positive terminal 
of the filament is permanently connected to the metal base of the 



tube, and connection is installed in the amplifier from the metal 
socket to the positive side of the filament resistance whereby the re¬ 
sistance is thus automatically short circuited when a tube of this 
type is inserted. These tubes are, however, no longer standard Sig¬ 
nal Corps equipment. 

50. Amplifier set boxes type BC-44 and BC-44-A.—These amplifiers 
are identical except that the BC-44-A, whose circuit, as shown in 
figure 14, is provided with only one pair of input terminals, whereas 
the BC-44 is provided with two pairs similar to the BC-17 set box. 
These amplifiers are similar to the BC-17 amplifier, except that a 
rheostat is provided in the filament circuit; no provision is made to 



















































AMPLIFIERS AND HETERODYNES. 25 

use any except the total amplification that can be produced by the 
set, and the plate voltage is 40 volts instead of 20 volts. 

51. Amplifier set box type BC-8-A.—This is an amplifier having three 
stages of radio frequency amplification followed by detection and 
two stages of audio frequency amplification. The circuits are shown 
in figure 15. 

The radio frequency signal impressed on the grid of the first tube 
appears in amplified form as a radio frequency component of the 
direct current in the plate circuit. The plate direct current is sup¬ 
plied by the 40-volt battery through the primary of a radio fre¬ 
quency iron core transformer. The impedance of the primary 
causes a radio frequency voltage to be set up across it by the radio 
frequency current. This voltage is stepped up by the secondary 
winding because of its larger number of turns, and this increased 
voltage is then impressed on the grid. The second and third radio 
frequency amplifier tubes and the third radio frequency amplifier 
tube and the detector tube are coupled together in the same manner 
by radio frequency iron core transformers. 

Radio frequency transformers operate best over a certain range of 
wave length. The transformers used in this amplifier operate well 
between 750 and 1,500 meters. Due to the fact that stray coupling 
always exists between the plate and grid circuits of an amplifier, 
the amplifier tends to generate oscillations. Such oscillations occur 
at that frequency at w'hich the total losses of the amplifier are a 
minimum. This condition is also that at which maximum amplifica¬ 
tion is obtained. As the quality of the signal received is very poor 
when the amplifier is oscillating, it is desirable to operate the am¬ 
plifier at the point just short of that at which oscillations occur, 
as it is at this point that the best readable signals are obtained. One 
of the factors that determines whether or not a tube will generate 
oscillations is the plate resistance. By adjusting the plate resistance 
the tube may, if other conditions permit, be brought to the point 
just short of oscillating. In order to secure this critical adjustment a 
rheostat is placed in series with the filaments of the radio frequency 
amplifier tubes. By varying the filament current the electron emis¬ 
sion is varied. This changes the plate resistance and hence gives a 
control over one of the factors producing oscillations. The filament 
circuits of the three radio frequency amplifier tubes each contain a 
0.5-ohm resistance, the common filament rheostat furnishing the bal¬ 
ance of the resistance necessary in the filament circuits. 

The transformers in the plate circuit of the third radio frequency 
amplifier tube has its secondary connected in series with the grid 
circuit of the detector tube. The detector tube circuit is of the type 
using a gridleak resistance and a condenser. The grid circuit is 
connected to the filament circuit so that the voltage drop across the 


26 


AMPLIFIERS AND HETERODYNES, 



COUPLING TRANSFORMER COUPLIN<i TRANSFORMER, 













































































































AMPLIFIERS AND HETERODYNES. 


27 


1.0-ohm resistance in the filament circuit places a positive biasing 
potential upon the grid. This potential is supplied through a 2- 
megohm gridleak resistance. The positive biasing potential causes a 
steady grid current to flow, the value of the current being such that 
the operation is located at the greatest bend of the grid current-yW^Z 
voltage curve (using proper plate voltage). The incoming radio 
frequency signal then undergoes an efiective rectification in the grid 
circuit. Because of the bend in the curve, the positive half of the 
cycle causes an increase in current that is greater than the decrease 
in current caused by the negative half of the cycle. The radio fre¬ 
quency voltage therefore causes a pulsating direct current to flow 
through the grid condenser. The action of the condenser is to store 
up these radio frequency pulsations. The condenser is charged so 
that the side connected to the grid becomes negative. The only way 
the negative charge can be dissipated is by a current passing through 
the 2-megohm resistance. As the voltage across the condenser is 
very small, an appreciable length of time is required to discharge 
the condenser energy. This time lag causes the radio frequency 
charges to build up so that the condenser charges and discharges at 
the group or spark frequency. The plate voltage is sufficient to make 
available the full amplification of the tube. The negative voltages 
appearing on the grid at the group of spark frequency are reproduced 
as an alternating current component of the direct current in the 
plate circuit. The plate current is supplied from the 40-volt bat¬ 
tery, the primary of an audio frequency transformer being included 
in series with the battery. A radio frequency by-pass condenser of 
0.0015 m. f. capacity is provided across the transformer primary. 

The audio frequency current in the detector tube plate circuit has 
its potential stepped up by means of the audio frequency trans¬ 
former, so that the largest possible potential is impressed on the grid 
of the first audio frequency amplifier tube. The amplifier audio fre¬ 
quency current obtained in the plate circuit of that tube is again 
amplified in a similar manner by the second audio frequency ampli¬ 
fier tube. Telephone jacks are provided in the plate circuits of both 
tubes so that either one or two stages of audio frequency amplifica¬ 
tion can be used as desired. When only one stage is used the tele¬ 
phone head set is connected in series with the plate circuit of the first 
audio frequency amplifier tube, and the audio frequency transformer 
primary in that circuit is shorted. 

Provision is made for the use of only one stage of audio frequency 
amplification, because while increased amplification strengthens the 
signal, it also strengthens all interfering noises due to static, me¬ 
chanical vibrations, audio frequency induction from near-by elec¬ 
trical apparatus, etc. Often, therefore, a weaker signal can be read 
more easily because of the reduction of intensity of interfering noises. 

83564—22-3 



28 


AMPLIFIERS AND HETERODYNES. 


The current in the filament circuits of the two audio frequency 
tubes is limited to the proper value by 1 ohm resistances placed in 
each circuit. The potential drop across the resistance in the filament 
circuit of the tubes is used to furnish a negative biasing potential, 
which is applied to the grids of both audio frequency amplifier tubes. 

52. Amplifier set box type BC-101. —This detector-amplifier is a 
vacuum tube detector and two-stage audio frequency amplifier. 
The circuit diagram is shown in figure 16. A switch is provided to 
enable the detector tube to be disconnected, if desired, in order to 
use the detector tube which may be included in the radio-receiving 
set. When the switch is thrown to “Detector” the input binding 
post marked “ Grid ” is connected to the grid of the detector tube. 
When the switch is thrown to “Amplifier” the input binding post 
marked “ Grid ” is connected to one terminal of the primary of the 
first audio frequency transformer. The other side of the primary 
of this transformer is then connected to the input binding post 
marked “Fil.” The input binding posts are connected to the grid 
and filament of the detector tube when the switch is thrown to 
“Detector,” and are connected to the primary of the first audio 
frequency transformer when the switch is thrown to “Amplifier.” 
When the switch is thrown to “Amplifier” the filament circuit of 
the detector tube is opened. 

"VWien the switch is thrown to “Detector” the radio frequency 
voltages developed across the secondary circuit of the radio receiv¬ 
ing set are impressed directly between the grid and filament of the 
detector tube. The 1.05-ohm resistance in the detector tube filament 
circuit is used to place a proper negative biasing potential on the 
grid. The plate current for the detector tube is furnished from the 
40-volt battery through the primary of an audio frequency trans¬ 
former and a 0.5 megohm resistance. The resistance is by-passed 
for both audio and radio frequency currents by a 0.15 m. f. con¬ 
denser. The primary of the audio frequency transformer is by¬ 
passed for radio frequencies by a 0.005 m. f. condenser. The effective 
value of plate voltage and the value of negative biasing potential on 
the grid are such that the value of plate current obtained is located 
on the greatest bend of the grid voltage flate current curve. This 
causes one-half of the radio frequency cycle to be amplified more 
than the other half of the cycle. An audio frequency current is 
thereby set up having the frequency of the spark signal or the 
heterodyne beat note signal. 

Two binding posts are provided in series with the plate circuit of 
the detector tube. The binding posts are normally connected to¬ 
gether, but the connecting strap may be removed and a tickler coil 
forming part of the radio receiving set connected between the bind- 


AMPLIFIERS AND HETERODYNES. 


29 


o 



























































30 


AMPLIFIERS AND HETERODYNES. 


iiig posts. By means of the tickler coil the detector tube circuit can 
be made regenerative for the purpose of strengthening spark or 
other damped wave signals, or can be made to oscillate for the pur¬ 
pose of heterodyning undamped wave signals. 

When the switch is thrown to “ Amplifier ” the audio frequency 
voltages developed in the plate circuit of the detector tube forming 
part of the radio receiving set are impressed across the primary of 
the audio frequency transformer connected to the first audio fre¬ 
quency amplifier tube. 

The operation of the audio frequency amplifier tube is the same 
whether the detector circuit forming part of BC-101 or a separate 
detector is used, and is analogous to the low-frequency stages of the 
BC-8-A amplifier. The current in the filament circuits of the three 
tubes is limited to the proper value for the VT-1 tube operated from 
a 4-volt battery by means of a 1.05-ohm resistance placed in each 
circuit. The potential drop across this fixed resistance in the fila¬ 
ment circuit of each tube is used to furnish a negative grid biasing 
potential. It wall be noted that the normal operating current for 
VT-1 tube filaments is determined by the 1.05-ohm fixed resistance 
in the circuit of each tube, with the filament control rheostats turned 
clockwise until the resistance is all cut out. 

Type VT-5 tubes require 0.25 ampere at 1.1 volts. IVhen VT-5 
tubes are used in the BC-101, a 2-volt storage battery or one closed 
circuit (ignition) type dry cell (1.4 volts) is connected to the fila¬ 
ment battery binding posts. The detector tube filament circuit con¬ 
tains a rheostat providing a maximum resistance of 10 ohms. The 
two amplifier tube filament circuits are supplied through a common 
rheostat providing a maximum resistance of 5 ohms. The rheo¬ 
stats provide ample resistance range for operating the VT-5 tubes 
from the battery sources mentioned above. The detector tube and 
amplifier tubes are supplied through separate rheostats because the 
detector tube may require a slightly different value of current for best 
operation than the value required for amplifier tubes. A control of 
amplification, using either VT-1 or VT-5 tubes, is obtained by vary¬ 
ing the filament control rheostat in the circuit of the amplifier tubes. 

53. Amplifier set box, type BC-103.—This is an amplifier having 3 
stages of radio frequency amplification, followed by a detector and 
2 stages of audio frequency amplification. By means of a switch 
and separate terminals provision is made for the use of only the 
audio frequency amplification when desired. When thrown to the 
audio amplification position, the switch opens the filament circuit 
of the four tubes that are not in use. The circuit diagram is shown 
in Fig. 17. The amplifier resembles the BC-8-A amplifier. It dif¬ 
fers mainly in that a control in addition to the filament control is 


CIRCUIT DIAGRAM 
AMPLIFIER TYPE BC-103 


AMPLIFIERS AND HETERODYNES. 


31 



A-b--AO-b + 





















































































































32 


AMPLIFIERS AND HETERODYNES. 


given to the high frequency amplifiers, and in that no grid-leak and 
condenser are used in the grid circuit of the detector tube. 

As has been stated greatest amplification is obtained when the 
amplifier is oscillating, but as this gives signal of poor quality, it is 
desirable to arrange the amplifier constants so that the amplifier is 
just at the point of oscillating, at' which point the best readable sig¬ 
nals are obtained. These constants will vary with different wave 
lengths and hence controls are necessary. In addition to the filament 
rheostat control found in the BC—8-A, there is a voltage divider 
(potentiometer) which is controlled from the panel. By means of 
this voltage divider, the average potential of the grid may be varied. 
Varying the potential of the grid varies the plate resistance of the 
tubes and hence, within limits, it is possible by this means to bring the 
amplifier to the point of oscillating. 

The transformer in the plate circuit of the third radio frequency 
amplifier tube has its secondary connected directly between the grid 
and filament of the detector tube. The 1.0 ohm resistance in the de¬ 
tector tube filament circuit is used to place a proper negative biasing 
potential on the grid. The plate current for the detector tube is 
furnished from the 40-volt battery through the primary of an audio 
frequency transformer and a 0.5 megohm resistance. The resistance 
is by-passed for both audio and radio frequency currents by a 0.35 
m. f. condenser. The primary of the audio frequency transformer 
is by-passed for radio frequencies by a 0.015 m. f. condenser. The 
effective value of plate voltages and the value of negative biasing 
potential on the grid are such that the value of plate current obtained 
is located on the greatest bend of the grid voltage-plate current curve. 
This causes one-half of the radio frequency cycle to be amplified 
more than the other half of the cycle. An audio frequency current 
is thereby set up having the frequency of the spark signal or the 
heterodyne beat note signal. 

54. Heterodyne set box, type BC-104.—In order to cause a tube to os¬ 
cillate it is necessary to couple the grid and plate circuit in such a 
manner that the transfer of energy from the plate to the grid circuit 
will compensate for all losses in the grid circuit. Inductive coupling 
is used for this purpose in the BC-104, whose circuit diagram is 
shown in figure 18. Frequency of oscillation is determined in the 
heterodyne by the grid circuit, which contains a variable air con¬ 
denser, Cl, and an inductance variable in two steps. The condenser, 
C 2 , is placed across the terminals of the plate battery and furnishes 
a by-pass for the oscillations in the plate circuit. It is to be noted 
that the coil transferring energy to the output circuit is the grid 
coil. The heterod 3 me is so designed that oscillation will be started 
as soon as the filament current is turned on. The oscillations are 


AMPLIFTEES AND HETERODYNES. 


33 


O 2^ 
J uu 
^0[xl< 
Lj U 0;: _J 

>-a:oQQ 


I 


O 

6 

< LiJ 

q: Cl 

o)- 

<h 


Q 

2 ' • ' 

lU ^ 

O - 

UJ 3 

-J ^ 

9E 

t h ^ 

- 

o <^^5^ 

I — o ^ 

^ua< 

<<90 

d-jo: ^ 

U. (L O Z 


Q 

2 

LJ 

O 

UJ 

-J 

(O 

D 

!< 

OH 

(L 

< 


0^ 

UJ 

<n 
2 
UJ 

o 
z 
o 
o 

< 

u 

-J 
OO 

<cc 

5 UJ 

<r ^ ^ 

5z,r>s p 

Ll Q — V) I 3 

s:zgg3^ 

^<JO w ^ t 

olilZZ<(j 

§882|c: 

i i I I I I 

— ^ M — — - (M 

u o -J ft: V) (O 


hx 

U1 V)> 


•0+ 



4V. 40V. • FIG. 18. 




















3i 


AMPLIFIERS AND HETERODYNES. 


strong enoiigli to persist under any operating conditions that may 
occur in the receiving antenna circuit. 

As is well known, the heterodyne method of reception consists of 
generating local oscillations, which, added to the incoming signal 
oscillation, produces a beat note which may be made of audible fre¬ 
quency. The local oscillation added to the incoming oscillation has 
the etfect. of amplifying it. The amplitude of the local amplification 
which produces the greatest effective amplification depends upon the 
amplitude of the incoming signal and to some extent upon the design 
of the receiving and detecting apparatus. The amplitude of the local 
oscillation which is added to the received oscillation may be varied 
by varying the coupling between the heterodyne and receiving cir¬ 
cuits. A control handle is provided for this purpose. 

In addition to the many advantages possessed by the beat method 
of reception, the method of using a heterodyne for this purpose has 
the following advantages over the method which uses an autodyne: 
In using an autodyne there must be a close reactance coupling be¬ 
tween the grid and plate circuits of the autodyne tube, and hence 
interfering signals, especially spark, will be amplified. In using an 
autodyne it must be slightly detuned in order to produce beats of 
desired frequency; this weakens the incoming oscillations. A 
heterodyne can also be calibrated and used as a wave meter. 

Section XI. 


PARTS LIST OF SETS. 

Paragraph. 


Equipments in complete sets_ 55 

Parts list of equipments_ 56 


55. Equipments in complete sets.—The equipments forming the com¬ 
plete sets of the amplifiers and heterodynes described in this pam¬ 
phlet are as follows: 

Set T. P. S. receiving, type SCR-72: 

Equipment, type GD-3. 

Equipment, type PE>-12. 

Equipment, type RC-3. 

Set T. P. S. receiving, type SCR-72-B: 

Equipment, type GD-3-A. 

Equipment, type PE-10. 

Equipment, type RC-3-B. 

Set low frequency amplifier, type SCR-121: 

Equipment, type PE-10. 

Equipment, type RC-11. 

Set low frequency amplifier, type SCR-121-B: 

Power equipment, type PE-38. 

Amplifier equipment, type RC-ll-B. 

Amplifier set, type SCR-144: 

Power equipment, type PE-38. 

Amplifier-equipment, type RE-24. 




AMPLIFIERS AND HETERODYNES. 


35 


Amplifier set, type SCR-145: 

Power equipment, type PE-38. 

Amplifier equipment, type RE-25. 

Heterodyne set, type SCR-146: 

Power equipment, type PE-38. 

Pleterodyne equipment, type RE-26. 

Amplifier set, type SCR-147: 

Power equipment, type PE-38. 

Amplifier equipment, type RC-3-A. 

Amplifier set, type SCR-148: 

Power equipment, type PE-38. 

Amplifier equipment, type RE-27. 

Amplifier set, type SCR-149: 

Power equipment, type PE-38. 

Amplifier equipment, type RE-28. 

56. Parts list of equipments.—The equipments listed in the paragraph 
above comprise parts as follows: 

Power equipment, type PE-10: 

Battery, type BB-14 (3)—1 in use, 2 spare. 

Power equipment, type PE-12: 

Battery, type BB-2 (2)—1 in use, 1 spare. 

Power equipment, type PE-38: 

Battery, type BB-28 (2)—1 in use, 1 spare. 

Radio equipment, type RC-3: 

Battery, type BA-2 (4)—2 in use, 2 spare. 

Case, type CS-2 (1). 

Cord, type CD-22 (1). 

Headset, type P-11 (2). 

Radio Communication Pamphlet No. 9 (1). 

Set box, type BC-17 (1). 

Tube, type VT-1 (4)—2 in use, 2 spare. 

Amplifier equipment, type RC-3-A: 

Battery, type BA-2 (4)—2 in use, 2 spare. 

Case, type CS-2 (1). 

Cord, type CD-50 (1). (Equipped with terminal type TM-12-A instead 
of TM-12.) 

Cord, type CD-56 (1). 

Headset, type P-11 (2). 

Radio Communication Pamphlet No. 9 (1). 

Set box, type BC-17 (1). 

Tube, type VT-1 (4)—^2 in use, 2 spare. 

Radio equipment, type RC-3-B: 

Bag, type BG-13 (1). 

Battery, type BA-2 (4)—2 in use, 2 spare. 

Compass, watch, luminous dial (1). 

Cord, type CD-40 (2)—1 in use, 1 spare. 

Cord, type CD-56 (1). 

Headset, type P-11 (2). 

Pliers, 6-inch combination (1). 

Radio Communication Pamphlet No. 9 (1). 

Screwdriver, l^-inch blade, ^-inch tip (1). 


36 


AMPLIFIERS AND HETERODYNES, 


Radio equipment, type RC-3-B—Continued. 

Set box, type BC-44 (1). 

Tape, friction (4 pound). 

Tube, type VT-1 (4)—2 in use, 2 spare. 

Voltmeter, type I-IO (1). 

Radio equipment, type RG-11: 

Battery, type BA-2 (4)—2 in use, 2 spare. 

Cord, type CD^O (2)—1 in use, 1 spare. 

Cord, type CD-56 (1). 

Headset, type P-11 (2). 

Radio Communication Pamphlet No. 9 (1). 

Set box, amplifier, type BC-44-A (1). 

Tube, type VT-1 (4)—2 in use, 2 spare. 

Amplifier equipment, type RC-ll-B: 

Battery, type BA-2 (4)—2 in use, 2 spare. 

Cord, type CD-50 (2)—1 in use, 1 spare. (Equipped with terminal, type 
TM-12-A instead of TM-12.) 

Cord, type CD-56 (1). 

Headset, type P-11 (2). 

Radio Communication Pamphlet No. 9 (1). 

Set box, amplifier, type BC-44-A (1). 

Tube, type VT-1 (4)—2 in use, 2 spare. 

Amplifier equipment, type RE-24: 

Battery, type BA-2 or BA-8 (4)—2 in use, 2 spare. 

Cord, type CD-50 (1). (Equipped with terminal, type TM-12-A instead 
of TM-12.) 

Headset, type P-11 (2). 

Radio Communication Pamphlet No. 9 (1). 

Set box, amplifier, type BO-8-A (1). 

Tubes, type VT-1 (12)—6 in use, 6 spare. 

Amplifier equipment, type RE-25: 

Battery, type BA-2 or BA-8 (4)—2 in use, 2 spare. 

Cord, type CD-42 (1). 

Cord, type CD-50 (1). (Equipped with terminal, type TM-12-A instead 
of TM-12.) 

Headset, type P-11 (2). 

Radio Communication Pamphlet No. 9 (1). 

Set box, amplifier, type BC-103 (1). 

Tubes, type VT-1 (12)—6 in use, 6 spare. 

Heterodyne equipment, type RE-26: 

Battery, type BA-2 or BA-8 (4)— 2 in use, 2 spare. 

Cord, type CD-50 (1). (Equipped with terminal, type TM-12-A instead 
of TM-12.) 

Radio Communication Pamphlet No. 9 (1). 

Set box, heterodyne, type BC-104 (1). 

Tubes, type VT-1 (2)—^1 in use, 1 spare. 

Amplifier equipment, type RE-27: 

Bag, type BG-13 (1). 

Battery, type BA-2 (4)—2 in use, 2 spare. 

Cord, type CD-50 (1). (Equipped with terminal, type TM-12-A instead 
of TM-12.) 

Cord, type CD-56 (1). 

Headset, type P-11 (2), 


AMPLIFIERS AKD HETERODYNES. 


37 


Amplifier equipment, type RE-27—Continued. 

Radio Communication Pamphlet No. 9 (1). 

Set box, amplifier, type BC-44 (1). 

Tubes, type VT-1 (4)—2 in use, 2 spare. 

Amplifier equipment, type RE-28: 

Bag, type BG-45 (1). 

Battery, type BA-2 (4)—2 in use, 2 spare. 

Case, type CS-20 (1). 

Cord, type CD-50 (1). (Equipped with terminal, type TM-12-A instead 
of TM-12.) 

Cord, type CD-56 (1). 

Headset, type P-11 (2). 

Radio Communication Pamphlet No, 9 (1). 

Set box, amplifier, type BC-101 (1). 

Tubes, type VT-1 (6)—3 in use, 3 spare. 

Ground equipment, type GD-3 (used in T. P. S. sets) : 

Bag, type BG-3 (1). 

Drum, type DR-3 (2). 

Hammer, 2 lb. cross-peen (1). 

Reel, type RL-G (1). 

Stake, type GP^, or GP-6, or GP-14 (12). 

Wire, type W-4 (1,000 feet). 

Wire, type W-5 (60 feet). 

Ground equipment, type GD-3-A (used in T. P. S. sets) ; 

Bag, type BG-8 (1). 

Drum, type DR-3 (2). 

Hammer, 2 lb. cross-peen (1). 

Reel, type RL-6 (1). 

Stake, type GP-6. (12). 

Wire, type W-4 (1,000 feet). 

Wire, type W-5 (60 feet). 


SIGNAL CORPS PAMPHLETS. 


(CoiTected to February, 1922,) 

RADIO COMMUNICATION PAMPHLETS. 

(Formerly designated Radio Pamphlets.) 

No. 

1. Elementary Principles of Radio Telegraphy and Telephony (edition of 

4-28-21) (W. D. D. No. 1064). 

2. Antenna Systems. 

3. Radio Receiving Sets (SCR-54 and SCR-54-A) and Vacnnm Tube Detector 

Equipment (Tyi>e DT1-3-A). 

5. Airplane Radio Telegraph Transmitting Sets (SCR-65 and SCR-Go-A). 

9. Amplifiers and Heterodynes (W. D. D. 1092). 

11. Radio Telegraph Transmitting Sets (SCR-74; SCR‘-74-A). 

13. Airplane Radio Telegraph Transmitting Set (Type SCR-73), 

14. Radio Telegraph Transmitting Set (Type SCR-69). 

17. Sets, U. W. Radio Telegraph (Types SCR-79^A and SCR-99) (W. D. D. 
1084). 

20. Airplane Radio Telephone Sets (Types SCR-68; SCR-68-A; SCR-114; 
SCR-116; SCR-59; SCR-59-A; SCR-75; SCR-115). 

22. Ground Radio Telephone Sets (Types SCR-67; SCR-67-A) (W. D. D. 1091). 

23. U. W. Airplane Radio Telegraph Set (Type SCR-80). 

24. Tank Radio Telegraph Set (T^^e SCR-78-A). 

25. Set, Radio Telegraph (Tj^e SCR-105) (W. D. D. 1077). 

26. Sets, IT. W. Radio Telegraph (Types SCR-127 and SCR-130) (W. D. D. 

1056) (edition of Nov., 1921). 

28. Wavemeters and Decremeters (W. D. D. 1094). 

30. The Radio Mechanic and the Airplane. 

40. The Principles Underlying Radio Communication (edition of May, 1921) 
(W. D. D. 1069). 

WIRE COMMUNICATION PAMPHLETS. 

(Formerly designated Electrical Engineering Pamphlets.) 

1. The Ruzzerphone (Type EE-1). 

2. Monocord Switchboards of Units Type EE>-2 and EiB-2-A and Monocord 

Switchboard Operator’s Set Type EE-64 (W. D. D. 1081). 

3. Field Telephones (Types EE-3; EE-4; EE-^). 

4. Laying Cable in the Forward Area (formerly designated Training Pamphlet 

No. 3). 

6. Trench Line Construction (formerly designated Training Pamphlet No. 6-a). 

7. Signal Corps Universal Test Set Type BE-65 (edition of Dec., 1921) (W. 

D. D. 1020). 

10. Wire Axis Installation and Maintenance Within the Division (W. D. D. 

1068). 

11. Elements of the Automatic Telephone System (W. D. D. 1096). 

TRAINING PAMPHLHTS. 

1. Elementary Electricity (edition of 1-1-21) (W. D. D. 1055). 

2. Instructions for using the cipher device Type M-94. (W. D. D. 1097.) 

(For official use only.) 

4. Visual Signaling. 

7. Primary Batteries (formerly designated Radio Pamphlet No. 7). 

8. Storage Batteries (formerly designated Radio Pamphlet No. 8). 

FIELD PAMPHLETS. 

1. Directions for Using the 24-CM. Signal Lamp (Type EEi-7). 

2. Directions for Using the 14-CM. Signal Lamp (Type EB-6). 

38 


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